Reaction products of imidazole on pyrazole derivatives and 4-isopropenyl-1-cyclohexene-1-carboxaldehyde

ABSTRACT

Thermosettable prepolymers or resins are prepared by reacting (1) a pyrazine compound containing at least two substituent groups which have a hydrogen atom attached to a carbon atom which is attached to the ring such as tetramethylpyrazine, (2) a material containing at least two aromatic aldehyde groups, and (3) at least one of (a) a nitrogen containing aromatic heterocyclic compound containing at least one hydrogen atom attached to a carbon atom attached to the ring and a polymerizable unsaturated group such as 2-methyl-5-vinylpyridine or (b) an aldehyde containing at least one polymerizable unsaturated group such as 4-isopropenyl-1-cyclohexene-1-carboxaldehyde. These prepolymers or resins are curable to thermoset products having good mechanical and thermal properties by heat and pressure or by homopolymerization or copolymerization with N,N&#39;-bis-imides such as 1,1&#39;-(methylenedi-4,1-phenylene)-bismaleimide. The prepolymers are suitable for preparing composites.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application of application Ser. No. 07/300,462filed Jan. 23, 1989 now U.S. Pat. No. 4,927,932, which is a division ofapplication Ser. No. 168,297 filed Mar. 15, 1988 now U.S. Pat. No.4,831,737 which is a division of application Ser. No. 840,190 filed Mar.17, 1986 (now U.S. Pat. No. 4,755,600) which is a division ofapplication Ser. No. 726,555 filed Apr. 23, 1985 (now U.S. Pat. No.4,629,770).

BACKGROUND OF THE INVENTION

The present invention pertains to polymers prepared from substitutedpyrazines containing at least one substituent group having a hydrogenatom attached to a carbon atom attached to the ring, aromaticpolyaldehydes and aldehydes or a nitrogen containing heterocycliccompound containing at least one substituent group having a hydrogenatom attached to a carbon atom attached to the ring and a polymerizableunsaturated group.

A copending application Ser. No. 670,428 entitled "THERMOSETTABLEPOLYMERS OR PREPOLYMERS PREPARED FROM POLYMETHYLATED PYRAZINES ANDAROMATIC POLYALDEHYDES AND CURED PRODUCTS THEREFROM" filed Nov. 9, 1984by Duane S. Treybig and Loren L. Swearingen discloses thermosettablepolymers prepared by reacting an alkyl substituted pyrazine with adialdehyde. The cured prepolymer has excellent properties at elevatedtemperatures as well as a high char yield (61% to 71%) in nitrogen.These properties of the resin are particularly suitable for thepreparation of graphite fiber composites or other cured articles whichmay be subjected to fire. However, these thermosettable prepolymers arecured by a condensation reaction which generates water. This watervaporizes during cure and produces undesirable voids and/or surfaceimperfections in the composite or other cured article.

These prepolymers can be terminated with an ethenyl (vinyl) substitutedmono-aldehyde or a vinyl and alkyl substituted aromatic heterocycliccompound. The resulting vinyl terminated polystyrylpyrazine prepolymerscan then be cured by an addition reaction via the unsaturated terminalgroups, thereby eliminating the release of water vapor and resulting incomposites or other cured articles which do not possess surfaceimperfections.

The vinyl terminated polystyrylpyrazine prepolymers of the presentinvention are also suitable as novel comonomers for reaction withN,N'-bis-imide resins. The copolymerization of the vinyl terminatedprepolymers with N,N'-bis-imide resins occurs at a lower curetemperature than that of a maleimide resin alone, which results inenergy conservation. Since the copolymerization is an addition reaction,volatile generation is minimized. The copolymers are more amorphous,less brittle, less crystalline and tougher polymers than N,N'-bis-imidepolymers Depending upon the choice of the vinyl termination molecule,the char yield of the resultant copolymer is higher than the char yieldof the cured N,N'-bis-imide on pyrolysis. As a consequence of the highchar yield of these copolymers, they exhibit better fire resistance thanthe cured N,N'-bis-imides. Char yield is defined herein as the percentby weight of the polymer remaining after exposure to 950° C. during athermogravimetric analysis of the polymer in a nitrogen atmosphere.

SUMMARY OF THE INVENTION

One aspect of the present invention pertains to a thermosettable productwhich results from reacting

(A) a pyrazine compound containing at least two substituent groups whichhave at least one hydrogen atom attached to a carbon atom which isattached to the ring or mixture of such pyrazines;

(B) at least one material having at least two aldehyde groups; and

(C) at least one of

(1) a nitrogen containing aromatic heterocyclic compound containing atleast one hydrogen atom attached lo a carbon atom attached to the ringand a polymerizable unsaturated group;

(2) an aldehyde containing at least one polymerizable unsaturated group;or

(3) a combination thereof;

and wherein components (A), (B) and (C) are employed in quantities whichprovide a mole ratio of (B):(C):(A) of from about 0.25:0.25:1 to about4:4:1, from about 0.5:0.5:1 to about 1.5:1.5:1.

Another aspect of the present invention pertains to the productsresulting from curing the aforementioned thermosettable reaction productby heat and pressure or by homopolymerization in the presence ofN,N'-bis-imides or copolymerization with a N,N'-bisimide.

Another aspect of the present invention pertains to the compositionresulting from reacting (A) a nitrogen containing aromatic heterocycliccompound containing at least one hydrogen atom attached to a carbon atomwhich is attached to the ring with (B) 4-isopropenyl-1cyclohexene-1-carboxaldehyde. These materials are useful herein asterminating agents.

DETAILED DESCRIPTION OF THE PREFERRED INVENTION

Suitable pyrazines which can be employed herein include any pyrazinewhich has at least two substituent groups which have at least onehydrogen atom attached to a carbon atom which is attached to the ring.Particularly suitable pyrazines include, di-, tri- and tetraalkylpyrazines such as, for example, 2,5-dimethylpyrazine,2,6-dimethylpyrazine, 2,3-dimethylpyrazine,3,5-dimethyl-2,6-pyrazinediamine, 2,3,5-trimethylpyrazine,2,3,5-trimethyl-6-pyrazinonitrile, 2-chloro-3,5,6-trimethylpyrazine,2,3,5,6-tetramethylpyrazine, 2,5-diethylpyrazine, 2,5-dipropylpyrazine,2,6-diethylpyrazine, 2,6-dipropylpyrazine, 2 3-diethypyrazine,2,3-dipropylpyrazine, 2,3,5-triethylpyrazine, 2,3,5-tripropylpyrazine,mixtures thereof and the like. 2-Methylpyrazine can be mixed or blendedwith pyrazine having two or more methyl groups to control the molecularweight of the prepolymer.

Other aromatic nitrogen containing heterocyclic compounds such aspyrazoles, pyridazines, pyrimidines, purines, pteridines, imidazoles,triazines, quinolines and quinoxalines having two or more substituentswhich have at least one hydrogen atom attached to a carbon atom which isattached to the ring can be mixed with or substituted for the pyrazineshaving such substituents. Suitable pyrazoles include3,5-dimethylpyrazole, 1-ethyl-3,5-dimethylpyrazole and3,4,5-trimethylpyrazole. Suitable pyridazines include3,5-dimethylpyridazine, 4-chloro-3,5-dimethypyridazine and3,4,5-trimethypyridazine. Suitable pyrimidines include2,4-dimethylpyrimidine, 4,5-dimethylpyrimidine, 4,6-dimethylpyrimidine,2,6-dimethyl-4-pyrimidinamine and 2,4,6-trimethylpyrimidine. Suitablepurines include 2,8-dimethylpurine, 2,8-dimethyl-6-purinamine, and2,6,8-trimethylpurine. Suitable pteridines include6,7-dimethylpteridine, 2,6-dimethylpteridine, 2,4,7-trimethylpteridine,and 2,4,6,7-tetramethylpteridine. Suitable imidazoles include2,5-dimethylimidazole, 2,4-dimethyimidazole and2,4,5-trimethylimidazole. Suitable triazines include3,5-dimethyl-1,2,4-triazine, 3,6-dimethyl-1,2,4-triazine,2,6-dimethyl-1,3,5-triazine and 2,4,6-trimethyl-1,3,5-triazine. Suitablequinolines include 2,6-dimethylquinoline, 2,7-dimethyquinoline,2,4-dimethylquinoline, 2,3,6-trimethylquinoline and2,3,6,7-tetramethylquinoline. Suitable quinoxaines include2,5-dimethylquinoxaline, 2,3-dimethylquinoxaline,2,6-dimethylquinoxaline, 2,3,7-trimethylquinoxaline and2,3,6,8-tetramethylquinoxaline. Pyrazole, pyridazine, pyrimidine,purines, pteridines, imidazoles, triazines, quinolines and quinoxalineshaving two or more of such substituents can be mixed or blended witheach other or pyrazine having two or more of such substituents. Also,pyridine having two or more of such substituents can be mixed or blendedwith pyrazine, pyrazole, pyridazine, pyrimidine, purines, pteridines,imidazoles, triazines, quinolines or quinoxalines having two or more ofsuch substituents or their mixtures.

Molecular weight control of the polymer can be obtained by the additionof an aromatic nitrogen containing heterocyclic compound having onesubstituent which has only one hydrogen atom attached to a carbon atomwhich is attached to the ring as a chain terminator to an aromaticnitrogen containing heterocyclic compound having two or moresubstituents which have at least one hydrogen atom attached to a carbonatom which is attached to the ring. For example, pyrazines, pyridines,pyrazoles, pyridazines, pyrimidines, purines, pteridines, imidazoles,triazines, quinolines, quinoxalines or a mixture of any two or more suchcompounds having at least one such substituent can be blended or mixedwith those having more than one such substituent.

Suitable aldehydes which can be employed herein include any aldehydeswhich contain at least two aldehyde groups and no other substituentgroups which would tend to interfere with the reaction of the aldehydegroups and the said substituent groups of the pyrazine material.Particularly suitable aldehyde materials include, for example, those ofthe formula: ##STR1## wherein n =2 or more, and R is an aromatic groupsuch as, for example, ##STR2## wherein R₁ is alkylene, oxygen, sulfur,oxyalkylene, polyoxyalkylene, ##STR3## wherein R₂ and R₃ are alkyl, arylor aralkyl, and substituted groups thereof.

Particularly suitable aldehydes include, for example,terephthadicarboxaldehyde, o-phthalicdicarboxaldehyde, isophthaladehyde,glyoxal, dicinnamylaldehyde, 2,5-pyrazinedicarboxadehyde,2,3,4,5-pyrazinetetracarboxaldehyde, 1,5-naphthalenedicarboxaldehyde,1,2,4,5,7,8-naphthalenehexacarboxaldehyde,1-bromo-2,5-naphthalenedicarboxaldehyde,2-hydroxy-1,5-naphthalenedicarboxaldehyde,2,6-phenanthrenedicarboxaldehyde, 2,7-pyrenedicarboxaldehyde,4-chloro-2H-thiochromene-3,7-dicarboxaldehyde,2,6-fluorenedicarboxaldehyde, 10-chloro-3,8-anthracenedicarboxaldehyde,3,7-quinolinedicarboxaldehyde, 4,4'-bisbenzene-1-carboxaldehyde,4,4'-oxy-bisbenzene-1-carboxaldehyde,4,4'-(2,1-ethanediylbisoxy)-benzene-1carboxaldehyde,4,4'-sulfonylbisbenzene-1-carboxaldehyde,4,4'-methyenebisbenzene-1-carboxaldehyde, and mixtures thereof.

Monoaldehydes such as benzaldehyde, o-tolualdehyde,trans-cinnamaldehyde, 3-chlorobenzaldehyde or p-anisaldehyde can hemixed or blended with a dialdehyde or mixture of dialdehydes to controlthe molecular weight of the prepolymer.

Pyrazine, pyrazole, pyridazine, pyrimidine, pyridine, purines,pteridines, imidazole, triazines, quinoline, and quinoxalines ormixtures thereof containing both a substituent having at east onehydrogen atom attached to a carbon atom which is attached to the ringand an aldehyde substituent can be reacted with itself. For example,suitable pyrazines containing both a substituent having at least onehydrogen atom attached to a carbon atom which is attached to the ringand an aldehyde substituent include 2-methyl-5-pyrazinecarboxaldehyde,2-methyl-6-pyrazinecarboxaldehyde 2-methyl-3,5-pyrazinedicarboxaldehyde,2,3-dimethy-5-pyrazinecarboxaldehyde and2,3-dimethyl-5,6-pyrazinedicarboxaldehyde.

Termination agents or compounds containing polymerizable unsaturatedgroups include ethenyl (vinyl) substituted monoaldehydes and aromaticheterocycles having both vinyl and alkyl groups. Suitable vinylsubstituted monoaldehydes include4-(1-methylethenyl)-1-cyclohexene-1-carboxaldehyde (perillaldehyde);5-norbornene-2-carboxaldehyde; 3-cyclohexene-1-carboxaldehyde;endo-bicyclo[3.1.0]hex-2-ene-6-carboxaldehyde; acrolein; crotonaldehyde;trans-2-hexenal; 2,4-hexadienal; trans,trans-2,4-heptadienal;trans,trans-2.4-,octadienal; trans,trans-2,4-nonadienal;3,7-dimethyl-2,6-octadienal; 4-ethenylbenzaldhyde;3,4-diethenylbenzaldehyde; 5-ethenylpyrazine-2-carboxaldehyde;6-ethenylpyrazine-2-carboxaldehyde; 5-ethenylpyridine-2-carboxaldehyde;4-(4-ethenylphenyl)-benzaldehyde; 4-(4-ethenylphenoxy)-benzaldehyde; andtheir mixtures.

Suitable aromatic heterocyclic compounds having both ethenyl (vinyl) andalkyl groups include 3-ethenyl-2-methylpyridine(2-methyl-3-vinylpyridine); 5-ethenyl-2-methylpyridine(2-methyl-5-vinylpyridine); 6-ethenyl-2-methylpyridine(2-methyl-6-vinylpyridine); 2-(buta-1,3-dienyl)-6-methylpyridine;2-(pent-1-enyl)-6-methylpyridine;2-(but-1,3-dienyl)-4,6-dimethylpyridine;2-methyl-4(prop-1-enyl)-pyridine;2-(6-(4-(1-methylethen-1-yl)cyclohex-1-enyl))-6-methylpyridine;2-(6-(4-(1-methylethen-1-yl)cyclohex-1-enyl))-4,6-dimethylpyridine;3,5-diethenyl-2-methylpyridine; 2,5-diethenyl-3,4-dimethylpyridine;3,5-diethenyl -2,4,6-trimethylpyridine;3-chloro-5-ethenyl-2,6-dimethylpyridine;5-ethenyl-6-ethyl-2-methylpyridine; 5-ethenyl-2-methyl-4-propylpyridine;3-ethenyl-2,6-diethylpyridine; 6-ethenyl-2,4-diethylpyridine;3-ethenyl-2-methylpyrazine (2-methyl-3-vinylpyrazine);5-ethenyl-2-methylpyrazine (2-methyl-5-vinylpyrazine);6-ethenyl-2-methylpyrazine (2-methyl-6-vinylpyrazine);5-ethenyl-2,6-dimethylpyrazine; 5-ethenyl-2,3,6-trimethylpyrazine;3,5-diethenyl-2,6-dimethylpyrazine; 5-ethenyl-2-ethyl-6 -methylpyrazine;5-ethenyl-2,6-diethylpyrazine; 2-methyl-5-(1-methylethenyl)pyrazine;2-(2-ethylbut-1-enyl)-6-methylpyrazine;2-methyl-6-(2-methylprop-1-enyl)pyrazine;2-(but-1,3-dienyl)-6-methylpyrazine;2-(pent-1-enyl)-3,6-diethylpyrazine;2-(but-1,3-dienyl)-3,6-dimethylpyrazine;2-methyl-5-(prop-1-enyl)pyrazine;2-(6-(4-(1-methylethen-1-yl)cyclohex-1-enyl))-6-methylpyrazine;2-(6-(4-(1-methylethen-1-yl)cyclohex-1-enyl))-5,6-dimethylpyrazine;2-(6-(4-(1-methylethen-1-yl)-cyclohex-1-enyl))-3,5,6-trimethylpyrazine;5-ethenyl-3-methylpyridazine; 4-chloro-5-ethenyl-3-methylpyridazine;5-ethenyl-3,6-dimethypyridazine; 4-ethenyl-2,6-dimethylpyrimidine;6-ethenyl-2-methyl-4-pyrimidinamine; 6-ethenyl-2,8-dimethylpurine;8-ethenyl-2,6-dimethylpurine; 6-ethenyl-8-ethyl-2-methylpurine;6-ethenyl-2-methyl-8-purinamine; 2-ethenyl-6,7-dimethylpteridine;6-ethenyl-2,4-dimethyl-1,3,5-triazine;5-ethenyl-3,6-dimethyl-1,2,4-triazine;5-ethenyl-3-methyl-6-propyl-1,2,4-triazine;7-ethenyl-2,4,8-trimethylquinoline;6,7-diethenyl-2,4,8-trimethylquinoline;6-ethenyl-2,3,8-tri-methylquinoxaline; 4-ethenyl-2,5-dimethylimidazole;4-ethenyl-3,5-dimethypyrazole and their mixtures.

The vinyl terminated polystyrylpyrazine prepolymers can be prepared bycondensing the alkyl substituted pyrazine, aldehyde and ethenyl (vinyl)termination agent in a one or two step process. The one step processcomprises condensing all three ingredients simultaneously. The two stepprocess comprises (1) condensing the alkyl substituted pyrazine andaldehyde to form polystyrylpyrazine oligomers and then (2) condensingthe polystyrylpyrazine oligomers with a vinyl termination agent. Thesereactions can be carried out neat or in the presence of a solvent. Asolvent is preferred. Dehydration conditions are suitably provided by adehydrating agent and/or a catalyst to activate the methyl groups. Inthe absence of a vinyl termination agent, the condensation is carriedout at a temperature of from about 50° to about 220° C., preferably from120° to 180° C. for about 1-48 hours (3600-172,800 s), especially 5-9hours (18,000-32,400 s). In the presence of a vinyl termination agent,the condensation is carried out at a temperature of from 50° to about140° C. preferably from 80° to 120° C. for about 1-48 hours(3600-172,800 s), preferably from 6 to 24 hours (21,600-86,400 s).

Suitable solvents include acids, amides, ketones, ethers, chlorinatedsolvents, aromatic heterocycles containing no alkyl substituents and thelike. Particularly suitable solvents include, glacial acetic acid,dimethylformamide, N,N-dimethylacetamide, N,N-dimethylformamide,N,N-dimethylmethoxyacetamide, hexamethylphosphotriamide,N-methyl-pyrrolidinone, tetrahydrofuran, pyridine, mixtures thereof andthe like.

Suitable catalyst include, for example, acids, Lewis acids, bases orsalts. Particularly suitable acids include, for example, sulfuric,hydrochloric or p-toluene-sulfonic acid. Particularly suitable basesinclude, for example, hydroxides of alkali or alkaline earth metals orof guaternary ammonium. Particularly suitable Lewis acids include, forexample, boron trifluoride and the like. Particularly suitable saltsinclude, for example, zinc chloride or aluminum chloride. The use ofsuch catalysts is not indispensable but it reduces the time required forthe reaction. The amount is e.g. of from about 0.1 to about 10 mole %with respect to the aromatic dialdehyde. If desirable, larger or lesserquantities can be employed.

Acceleration can occur with certain substances such as methyl iodide,methyl sulfate, benzyl chloride etc., which are capable of forming withthe pyrazinic base quaternary ammonium derivatives, such substancesbeing usable in catalytic amounts or higher proportions.

Dehydrating agents such as acetic anhydride, trifluoroacetic anhydride,propionic anhydride and the like can promote the reactions and itsaction can be sufficient to render superfluous the incorporation of acatalyst. The amount of anhydride used ranges from 1 to 10 moles permole of vinyl termination agent, preferably 1.1 to 5. The preferreddehydrating medium is a mixture of glacial acetic acid and aceticanhydride. The acetic acid and acetic anhydride can be removed bydistillation, solvent extraction, solvent fractionation or byneutralization with a base. Examples of several solvent fractionationmethods are described in U.S. Pat. Nos. 362,860 and 4,471,107 which areincorporated herein by reference. Suitable bases include sodiumhydroxide, ammonia hydroxide and ammonia.

The reactions are usually conducted either under reduced pressure or inan inert atmosphere such as, for example, nitrogen, helium, neon, zenon,argon, mixtures thereof and the like.

The thermosettable prepolymers or resins of the present invention can becured as is with the application of heat and pressure, or they can bedissolved in a suitable solvent or mixture of solvent and employed tosaturate various reinforcing materials so as to prepare compositestherefrom through the application of heat and pressure.

Suitable solvents which can be employed for preparing these compositesinclude for example, ketones acetates, alcohols, ethers, hydrocarbonsand the like. Particularly suitable solvents include, for example,acetone, methylethylkeLone, ethyl acetate, methylene chloride,trichloroethylene, tetrahydrofuran, chlorobenzene, ethanol, n-propanolN-methyl-pyrrolidinone, dimethylformamide, dimethylacetamide,nitrobenzene, mixtures thereof and the like.

Suitable reinforcing materials include, for example, glass fibers,aramid fibers, carbon or graphite fibers and the like in any form suchas, for example, matt, woven or fibrous form. Any synthetic or naturalfiber materials can be employed as the reinforcing material.

The thermosettable prepolymers can be used according to variousconventional techniques applicable to thermosetting resins. Powderedprepolymers are especially adapted for shaping by pressure-molding, butthey can also be dissolved in a solvent or be employed in molten form.They can be used in the preparation of laminates or composites, moldedarticles, films, coatings and the like.

The thermosettable products of the present invention can be cured bycompression molding at a temperature of from about 100° C. to about 350°C. and a pressure up to about 10,000 psig.

The prepolymer is advantageously set by a thermal treatment at atemperature of from about 100° to about 300° C. Finally there isobtained a non-fusible and non-soluble polymer. Said polymer has a goodthermal stability.

The vinyl terminated prepolymer can be homopolymerized (blended) in thepresence of a N,N'-bis-imide or copolymerized with a N,N'-bis-imide ofthe formula: ##STR4## in which X represents a divalent radicalcontaining a carbon-carbon double bond and A is a divalent radicalhaving at least 2 carbon atoms Preferred N,N'-bis-imides which may beemployed include 1,1'-(1,2-ethanediyl)bis-1H-pyrrole-2,5-dione;1,1'-(1,6-hexanediyl)bis-1H-pyrrole-2,5-dione;1,1'-(1,4-phenylene)bis-1H-pyrrole-2,5-dione;1,1'-(1,3-phenylene)bis-1H-pyrrole-2,5-dione;1,1'-(methylenedi-4,1-phenylene)bis-1H-pyrrole-2,5-dione(1,1'-(methylenedi-4,1-phenylene)bismaleimide);1,1'-(oxydi-4,1-phenylene)bis-1H-pyrrole-2,5-dione;1,1'-(sulfonyldi-4,1-phenylene)bis-1H-pyrrole-2,5-dione;1,1'-(methylenedi-4,1-cyclohexanediyl)bis-1H-pyrrole-2,5-dione;1,1'-[1,4-phenylenebis(methlene)]bis-1H-pyrrole-2,5-dione;1,1'-(1,1-dimethyl-3-methylene-1,3-propanediyl)di-4,1-phenylene]bis-1H-pyrrole-2,5-dione;1,1'-[(1,3,3-trimethyl-1-propene-1,3-diyl)di-4,1-phenylene]bis-1H-pyrrole-2,5-dione;and Technochemie's H-795 resin. Technochemie's H-795 resin isrepresented by the formula: ##STR5## where R is an aromatic ring andX-R₁ -X is a Michael addition coupling group. Technochemie's M-751 resinis a "eutectic" mixture of ##STR6##

The following examples are illustrative of the present invention, butare not to be construed as to limiting the scope thereof in any manner.

EXAMPLE 1 (Preparation of a Pyrazine containing a PolymerizableUnsaturated Group)

2,3,5,6-Tetramethylpyrazine (79.96 g, 0.59 mole) and4-isopropenyl-1-cyclohexene-1-carboxaldehyde (94.61 g, 0.63 mole) wereheated with stirring in a 500 ml resin kettle equipped with a dryice-acetone cold trap, immersion thermometer, mechanical stirrer andnitrogen purge system. Sulfuric acid (2.00 g, 0.0204 mole) was addedafter complete dissolution which was apparent at 105° C. After 7 hoursand 18 minutes (26,280 s) between 105° -190° C., the reactor contentswere sampled.2-(2-(4-(1-methylethen-1-yl)cyclohex-1-enyl)ethenyl)-3,5,6-trimethylpyrazine,##STR7## was identified in the reactor sample by electron impactcapillary chromatography mass spectrometry. The reactor contents wereheated for an additional 7 hours and 35 minutes (27,300 s) between 107°-193° C. The resultant reddish brown colored liquid was subjected torotary evaporation at 100° C. under full vacuum.

EXAMPLE 2

2,3,5,6-Tetramethylpyrazine (38.2 g, 0.28 mole),terephthaldicarboxaldehyde (57.2 g, 0.43 mole), and acetic acid (51.9 g,0.86 mole) were weighed into a 500 ml resin kettle equipped with animmersion thermometer, mechanical stirrer, nitrogen gas purge andcondenser. After the reactants were stirred and deoxygenated for fiveminutes (300 s), acetic anhydride (87.2 g, 0.85 mole) was added to theresin kettle The reactants were heated to 142° C. and allowed to refluxfor 4 hours and 2 minutes (14,520 s). The reaction mixture was cooled to97° C. and the rotary evaporation product from the reaction of2,3,5,6-tetramethylpyrazine and4-isopropenyl-1-cyclohexene-1-carboxaldehyde in Example 1 (55.2 q) wasadded to the resin kettle The reactants were heated between 107° -114°C. for an additional 7 hours and 22 minutes (26,520 s). While theresultant red orange colored liquid was cooling, the reactor contentswere neutralized with an aqueous solution of 9.6 wt/wt % of sodiumhydroxide (793 g). The sodium hydroxide solution was decanted, deionizedwater (761 g) added to the orange prepolymer, the resultant contentsstirred for 35 minutes (2100 s) and the water decanted The prepolymerwas washed twice more with water. The prepolymer was dissolved intetrahydrofuran and filtered. The filtrant was discarded, while thefiltrate was rotary evaporated at 100° C. under full vacuum. Theresultant red-orange viscous liquid was dried between 90°-98° C. underfull vacuum for 14 hours and 15 minutes (51,300 s). The resulting softred orange solid was analyzed by proton ('H) nuclear magnetic resonance(NMR) spectroscopy to verify the structure of the prepolymer. Theterminal isopropenyl (H₂ C═C>) proton, the cyclohexene vinyl (--CH═C>)proton, and the aromatic and internal vinyl (--CH═CH--) protons wereobserved absorbing at 4.1-4.3, 6.4, and between 6.9-7.6 ppm,respectively. Two and five tenths percent of the total protons wereterminal isopropenyl (H₂ C═C>) protons. The experimentally determinedproton distribution of the isopropenyl terminated prepolymer isconsistent with n=2, ##STR8##

EXAMPLE 3

The red orange isopropenyl terminated polystyrylpyrazine prepolymerprepared in Example 2 was oven cured between 95°-155° C. under fullvacuum for 16 hours and 40 minutes (60,000 s Gel permeationchromatography based upon polystyrene standards indicated the weightaverage molecular weight of the isopropenyl terminated prepolymer was623. The prepolymer was oven cured an additional 3 hours and 40 minutes(13 200 s) between 155°-263° C. The resulting red orange solid wascrushed with a mortar and pestle and then sieved with a U.S.A. StandardTesting Sieve No. 40 to give a fine red orange powder. The isopropenylterminated prepolymer softened at 155° C. The red orange isopropenylterminated prepolymer was compression molded between 192°-198° C. and3550-4000 psi (24,477-27,580 kPa) for 1 hour (3600 s) and between257°-265° C. and 3700-3800 psi (25,512-26,201 kPa) for another hour(3600 s) with a Carver Laboratory press, employing a silicone moldrelease agent. Thermogravimetric analysis of the cured black polymer innitrogen showed 5% weight loss at 420° C. and 50.1% weight loss at 950°C. In air, the polymer lost 5% weight at 420° C. Dynamic mechanicalanalyses was performed between -160° C. to 400° C. in the torsionalrectangular mode with a oscillatory frequency of 1 hertz and 0.05%strain. The polymer exhibited a gamma transition (T.sub.γ) temperatureat -120° C. and storage modulus (G') of 1.779×10¹⁰ dynes/cm² at 25° C.

EXAMPLE 4

The red orange isopropenyl terminated polystyrylprazine prepolymerprepared in Example 2 was oven cured between 115°-187° C. under fullvacuum for 2 hours and 58 minutes (10 680 ) and then between 79°-265° C.under full vacuum for 16 hours and 19 minutes (58,740 s). Theisopropenyl terminated polystyrylpyrazine prepolymer softened between157°-180° C.

1,1'-(Methylenedi-4,1-phenylene)bismaleimide was oven cured under fullvacuum between 186°-219° C. for 17 minutes (1020 s). The oven cured1,1'-(methylenedi-4,1-phenylene)bismaleimide softened at 158° C. This1,1'(methylenedi-4,1-phenylene)bismaleimide (13 g) and the oven curedisopropenyl terminated polystyrylpyrazine prepolymer (13 g) were mixedto give a brown powder. This powder was compression molded between187°-195° C. and 6980-7350 psi (48,127-50,678 kPa) for one hour and 2minutes (3720 s) and between 262°-264° C. and 7020-7050 psi(48,403-48,610 kPa) for another hour (3600 s) with a Carver Laboratorypress as described in Example 3 Thermogravimetric analysis of the curedblack polymer in nitrogen showed 5% weight loss at 440° C. and 51.5%weight loss at 950° C. In air, the polymer lost 5% weight at 452° C.

EXAMPLE 5

2,3,5,6-Tetramethylpyrazine (45.5 g, 0.33 mole),terephthaldicarboxaldehyde (67.4 g, 0.50 mole) and acetic acid (61.5 g,1.02 mole) were weighed into a 1 liter resin kettle equipped with animmersion thermometer, mechanical stirrer, nitrogen gas purge andcondenser. After the reactants were deoxygenated by stirring for fiveminutes (300 s) in a nitrogen atmosphere, acetic anhydride (103.6 %,1.01 mole) was added to the resin kettle. The reactants were heated to1%3° C. and allowed to reflux for 6 hours and S3 minutes (24,780 s. Thenthe reaction mixture was cooled to below 100° C. and2,3,5,6-tetramethylpyrazine (68.7 g, 0.50 mole), and4-isopropenyl-1-cyclohexene-1-carboxaldehyde (73.0 g, 0.49 mole) wereadded to the resin kettle. The reactor contents were heated between132°-136° C. for an additional 23 hours and 20 minutes (84,000 s). Asthe resultant red orange colored liquid was cooled to room temperature,the stirring reactor contents were neutralized with an aqueous solutionof 9.7 wt/wt % of sodium hydroxide (924% g . The sodium hydroxidesolution was decanted, deionized water (1056 g added to the burgundycolored isopropenyl terminated polystyrylpyrazine prepolymer theresultant contents stirred for 1 hour 54 minutes (6,840 s) and the waterdecanted. The isopropenyl terminated prepolymer was washed twice morewith water (2400 %) The burgundy solid was dried in an oven under fullvacuum between 123°-135° C. for 1 hour and 44 minutes (6,240 s) and thenbetween 172°-250° C. for 3 hours and 13 minutes (11,580 s). Aftercooling to room temperature, the prepolymer was sieved with a U.S.A.Standard Testing Sieve No. 40. Gel permeation chromatography based uponpolystyrene standards indicated the weight average molecular weight ofthe isopropenyl terminated polystyrylpyrazine prepolymer was 2710. Theisopropenyl terminated prepolymer softened between 153°-172° C. In adifferential scanning calorimetry analysis, the burgundy prepolymersealed in a glass ampule exhibited an exotherm of 12.5 joules/gram thatstarted at 100° C., peaked at 146° C. and ended at 182° C. followed by asecondary exotherm of 166 joules/gram that started at 230° C., peaked at347° C. and ended at 396° C..

EXAMPLE 6

The isopropenyl terminated polystyrylpyrazine prepolymer (51 g)described in Example 5 was dissolved in tetrahydrofuran (73 g) byheating to a slight boil on a hot plate. The tetrahydrofuran solution ofisopropenyl terminated prepolymer was brushed onto a 14"×14" (35.6×35.6cm) woven graphite fiber mat (Hercules AP193 dry cloth) clamped to aframe. The graphite fiber mat preimpregnate was allowed to dry overnightat room temperature. Then it was dried in an oven under full vacuumbetween 122°-155° C. for 29 minutes (1,740 s). The red orange prepolymerscraped off the graphite fiber mat preimpregnate soften between238°-254° C. Nine 4"×4" (10.1×10.1 cm) sections were cut from thegraphite fiber mat preimpregnate, layed up on top of one another andthen compression molded between 240°-248° C. and 550-2000 psi(3,792-13,790 kPa) for 1 hour (3600 s) and then between 246°-279° C. and580-700 psi (3,999-4,827 kPa) for 2 hours (7200 s) with a CarverLaboratory press. The finished composite had thoroughly fused giving abrown and flexible sample after trimming. Thermogravimetric analysis ofthe graphite composite in nitrogen showed 5% weight loss at 460° C. and19.5% weight loss at 950° C. The composite lost 5% weight at 386° C. and70% weight at 700° C. in air. Dynamic mechanical analyses showed noglass transition temperature up to 400° C., a gamma transition (T₆₅)temperature -113° C. and storage modulus (G') of 4.027×10¹⁰ dynes/cm² at25° C. Modulus retention at 200° and 300° C. with respect to the storagemodulus at 25° C. was 73 and 64%, respectively.

EXAMPLE 7

Technochemie Compimide 795 (a bismaleimide) was dried in an oven underfull vacuum between 100°-137° C. for 1 hour and 8 minutes (4,080 s). Thedried Technochemie compimide 795 (3.1 g) and the isopropenyl terminatedpolystyrylpyrazine prepolymer (3 1 g) described in Example S were mixedand crushed with mortar and pestle giving an orange brOWn powder. In adifferential scanning calorimetry analysis., the orange brown powdersealed in a glass ampule exhibited an exotherm of 139 joules/gram thatstarted at 100° C., peaked at 204° C. and ended at 262° C.. The driedTechnochemie compimide 795 alone exhibited an exotherm of 249joules/gram that started at 120° C., peaked at 249° C. and ended at 323°C. This differential scanning calorimetry experiment demonstrates thatthe isopropenyl terminated polystyrylpyrazine prepolymer lowered thecure temperature of the Technochemie compimide 795 by 45° C.

The mixture of the isopropenyl terminated polystyrylpyrazine andTechnochemie Compimide 795 was cured in an oven under full vacuumbetween 106°-158° C. for 57 minutes (3,420 s . After cooling to roomtemperature, the partially cured copolymer was a burgundy colored solid.It was crushed with a mortar and pestle to give an orange brown powderthat softens at 177° C. This powder was compression molded between187°-201° C. and 4700-5050 psi (32,407-34,820 kPa) for 1 hour (3600 s)and between 252°-264° C. and 4700-4950 psi (32,407-34,130 kPa) foranother hour (3600 s) with a Carver Laboratory press as described inExample 3. Thermogravimetric analysis of cured copolymer in nitrogenshowed 5% weight loss at 420° C. and 51.2% weight loss at 950° C. Inair, the copolymer lost 5% weight at 405° C. Dynamic mechanical analysesshowed a gamma transition (T.sub.γ) temperature at -106° C. and storagemodulus (G') of 2.22×10¹⁰ dynes/cm² at 25° C.

EXAMPLE 8

2,3,S,6-Tetramethylpyrazine (136.% g, 1.00 mole),terephthaldicarboxaldehyde (203.7 g, 1.52 moles) and acetic acid (184.27g, 3.07 mole) were weighed into a 2-liter resin kettle equipped with animmersion thermometer, mechanical stirrer, nitrogen gas purge system andcondenser. After the reactants were deoxygenated by stirring for fiveminutes (300 s) in a nitrogen atmosphere, acetic anhydride (307.4 g,3.01 mole) was added to the reactor. The reactants were heated to 142°C. and a11owed to reflux for 5 hours (18,000 s). After the reactionmixture was cooled to 98° C., 2-methyl-5-vinylpyridine (182.97 g,1.54mole) was added to the resin kettle The reactor contents were heatedbetween 93°-123° C. for an additional 9 hours and 14 minutes (33,2%0 s .As the burgundy colored liquid was cooling to room temperature, thereactor contents were neutralized with an aqueous solution of 9.99 wt/wt% sodium hydroxide (1701 g). The sodium hydroxide solution was decanted,deionized water (855 g) was added to the burgundy vinyl terminatedprepolymer and the water decanted Again water (1094 g) was added to theburgundy prepolymer and this mixture stirred for 51 minutes (3,060 s),the water was decanted, the prepolymer washed with water (876 g , thewater was decanted, water (1091 g) added to the prepolymer and themixture stirred for 2 hours (7200 s) and the water decanted giving aburgundy viscous liquid. Gel permeation chromatography indicated theweight average molecular weight of the 2-methyl-S-vinylpyridineterminated prepolymer was 554.

EXAMPLE 9

The burgundy viscous liquid from Example 8 was dried in an oven underfull vacuum between 80°-122° C. for 5 hours and 29 minutes (19,740 s)and oven cured under full vacuum between 118°-200° C. for 2 hours and 58minutes (10,680 s). The resultant sold was crushed with a mortar andpestle and then sieved with a U.S.A. Standard Testing Sieve No. 40 togive a fine burgundy powder. Gel permeation chromatography indicated theweight average molecular weight of the 2-methyl-5-vinylpyridineterminated prepolymer was 1602 The burgundy powder softened between133°-163° C. The burgundy 2-methyl-5-vinylpyridine terminated prepolymerwas compression molded between 170°-193° C. and 4200-4500 psi(28,959-31,028 kPa) for 1 hour (3600 s) and then between 220°-254° C.and 4300-4500 psi (29,649-31,028 kPa) for 1 hour 33 minutes (5,580 s)with a Carver Laboratory press, employing a silicone mold release agent.Thermogravimetric analysis of the cured polymer in nitrogen showed 5%weight loss at 390° C. and 41.0% weight loss at 950° C. In air, thepolymer lost 5% weight at 400° C. Dynamic mechanical analyses showed noglass transition temperature up to 400° C., a gamma transition (T.sub.γ)temperature at -104° C. and storage modulus (G') of 7.911×10⁹ dynes/cm²at 25° C.

EXAMPLE 10

The burgundy viscous liquid from Example 8 was dried in an oven underfull vacuum between 75°-127° C. for 8 hours and 31 minutes (30,660 s).The resultant solid was crushed with mortar and pestle to give a fineburgundy powder. Gel permeation chromatography indicated the weightaverage molecular weight of the 2-methyl-5-vinylpyridine terminatedprepolymer was 1657. In a differential scanning calorimetry analysis,the burgundy prepolymer exhibited an exotherm of 59.8 joules/gram thatstarted at 144° C., peaked at 228° C. and ended at 260° C. followed by asecondary exotherm that peaked at 348° C. The burgundy2-methyl-5-vinylpyridine terminated polystyrylpyrazine melted between68°-105° C. The 2-methyl-5-vinylpyridine terminated polystyrylpyrazineprepolymer (50.9 g was solubilized in tetrahydrofuran (45 g) by heatingto a slight boil on a hot plate. The tetrahydrofuran solution of2-methyl-5-vinylpyridine terminated polystyrylpyrazine prepolymer wasbrushed onto a 14"× 14"(35.6×35.6 cm) woven graphite fiber mat (HerculesAP193 dry cloth) clamped to a frame. The graphite fiber matpreimpregnate was allowed to dry overnight at room temperature. Then itwas dried in an oven under full vacuum between 120°-155° C. for 40minutes (2400 s) and between 167°-181° C. for 21 minutes (1260 s). Theburgundy prepolymer scraped off the graphite fiber mat preimpregnatesoften between 131°-195° C. Nine 4"×4" (10.1×10.1 cm) sections were cutfrom the graphite fiber mat preimpregnate, layed up on top of oneanother and then compression molded between 187°-235° C. and 1780-2580psi (12,273-17,789 kPa) for 1 hour (3600 s) and then between 231°-263°C. and 1800-1850 psi (12,411-12,756 kPa) for 2 hours (7200 s) with aCarver Laboratory press. The finished composite had thoroughly fusedgiving a dark brown, flexible sample after trimming. Thermogravimetricanalysis of the graphite composite in nitrogen showed 5% weight loss at447° C. and 28.2% weight loss at 950° C. The composite lost 5% weight at415° C. in air. Dynamic mechanical analysis showed no glass transitiontemperature up to 400° C., a gamma transition (T.sub.γ) temperature at-105° C. and storage modulus (G') of 4.136×10¹⁰ dynes/cm² at 25° C.Modulus retention at 200° and 300° C. with respect to the storagemodulus at 25° C. was 81 and 72%, respectively.

EXAMPLE 11

Technochemie compimide 795 was dried in an oven under full vacuumbetween 100°-137° C. for 1 hour and 8 minutes (4,080 s . The burgundy2-methyl-5-vinylpyridine terminated polystyrylpyrazine prepolymer fromExample 8 was dried in an oven under full vacuum between 87°-127° C. for7 hours and 7 minutes (25,620 s). Gel permeation chromatographyindicated the weight average molecular weight of the burgundy prepolymerwas 1220. The dried Technochemie compimide 795 (3 74 g) and the dried2-methyl-5-vinylpyridine terminated polystyrylpyrazine prepolymer (3.75g) were mixed and crushed with mortar and pestle giving an orange brownpowder. In a differential scanning calorimetry analysis, the orangebrown powder exhibited an exotherm of 197 joules/gram that started at100° C., peaked at 179° C. and ended at 270° C. The dried TechnochemieCompimide 795 alone exhibited an exotherm of 249 joules/gram thatstarted at 120° C., peaked at 249° C. and ended at 332° C. Thisdifferential scanning calorimetry experiment demonstrates that the2-methyl-5-vinylpyridine terminated polystyrylpyrazine prepolymerlowered the cure temperature of the Technochemie Compimide 795 by 70° C.

The mixture of dried Technochemie compimide 795 and dried2-methyl-5-vinylpyridine terminated polystyrylpyrazine prepolymer wascured in an oven under full vacuum between 106°-155° C. for 24 minutes(1440 s) and then between 1%7°-158° C. for 33 minutes (1980 s). Aftercooling to room temperature, the partially cured copolymer was aburgundy colored solid. The solid was crushed with a mortar and pestleto give a red orange powder that softened between 180°-200° C. Thispowder was compression molded between 197°-205° C. and between 5020-5300psi (34,613-36,544 kPa) for 1 hour and 6 minutes (3960 s) and thenbetween 242°-264° C. and 5060-5100 psi (34,889-35,165 kPa) for 53minutes (3180 s) with a Carver Laboratory press. Thermogravimetricanalysis of cured copolymer in nitrogen showed 5% weight loss at 375° C.and 48% weight loss at 950° C. In air, the copolymer lost 5% weight at370° C. Dynamic mechanical analyses showed no glass transitiontemperature up to 390° C., a gamma transition (T.sub.γ) temperature at-107° C. and storage modulus (G') of 1.055×10¹⁰ dynes/cm² at 25° C.

EXAMPLE 12

2,3,S,6-Tetramethylpyrazine (136 9, 1.0 moles),terephthaldicarboxaldehyde (201 g, 1 5 moles) and acetic acid (180 g, 3moles) were stirred in a 2-liter resin kettle equipped with a mechanicalstirrer, thermometer, nitrogen gas inlet and condenser. Afterdeoxygenation, acetic anhydride (306 g, 2.97 moles) was added to thereactor. The reactants were heated to 140° C. and allowed to reflux for6 hours and 14 minutes (29,640 s). The reaction mixture was cooled to100° C. and 2-methyl-5-vinylpyridine (179 g, 1.5 moles) was added to thereactor. The reactants were heated to 120° C. and allowed to reflux for8 hours and 14 minutes (29,640 s . On cooling to room temperature, thereactor product was a red-burgundy viscous liquid.

The red-burgundy product (187 %) was transferred to a 1-liter reactor,stirred and an 8% aqueous solution of sodium hydroxide was added untilthe product was neutralized. The sodium hydroxide solution was decanted,water added to the prepolymer, contents were stirred for an hour (3600s) and the water decanted. The prepolymer was twice more washed withwater. The prepolymer was dried by using vacuum filtration and 2-3 hours(7200-10,800 s) at 90° C. under full vacuum in an oven to give ared-burgundy solid. The red-burgundy solid was ground with mortar andpestle to give a red-burgundy powder that melted at 100° C. The infraredspectrum of the powder showed a band at 970 cm⁻¹ which indicates thepresence of trans unsaturation and a band at 910 cm⁻¹ which ischaracteristic of ═CH₂ wagging frequency for a vinyl group (R--CH═CH₂).The red-burgundy 2-methyl-5-vinylpyridine terminated polystyrylpyrazineprepolymer was sieved and then compression molded between 240°-275 ° C.and 6100 psi (42,060 kPa) for 2 hours (7200 s) with a Carver Laboratorypress, employing a silicone mold release agent. Thermogravimetricanalysis of the cured polymer in nitrogen showed 5% weight loss at 422°C. and 42% weight loss at 950° C. In air, the polymer lost 5% weight at397° C. Dynamic mechanical analyses showed no glass transitiontemperature up to 400° C., a gamma transition (T.sub.γ) temperature at-100° C. and storage modulus (G') of 1.220×10¹⁰ dynes/cm² at 25° C. Thecompression molded polymer was post cured for 15 hours between 255°-265°C. Thermogravimetric analysis in nitrogen showed 5% weight loss at 455°C. and 39% weight loss at 950° C. In air, the polymer lost 5% weight at405° C.

EXAMPLE 13

1,1'-(Methylenedi-4,1-phenylene)bismaleimide was oven cured under fullvacuum at 180° C. and sieved with a U.S.A. Standard Testing Sieve No.40. The resulting maleimide prepolymer softened between 200°-250° C. Themaleimide prepolymer (10 g) and the sieved red-burgundy 2-methyl-5-vinylpyridine terminated polystyrylpyrazine prepolymer (10 g)described in Example 12 were mixed to give a brown colored powder. Thispowder was compression molded between 235°-292° C. and between 5950-6100psi (41,025-42,060 kPa) for 2 hours (7200 s) with Carver Laboratorypress as described in Example 3. Thermogravimetric analysis of the curedblack polymer in nitrogen showed 5% weight loss at 386° C. and 46.5%weight loss at 950° C. In air, the polymer lost 5% weight at 400° C. and64% weight loss at 700° C. Dynamic mechanical analyses showed a gammatransition (T.sub.γ) temperature at -100° C. and storage modulus (G') of1.433×10¹⁰ dynes/cm² at 25° C.

I claim:
 1. A composition which results from reacting (A) nitrogencontaining aromatic heterocyclic compound having at least one hydrogenatom attached to a carbon atom which is attached to the ring selectedfrom the group consisting of imidazoles, pyrazoles or a combination ofany two or more of such compounds with (B)4-isopropenyl-1-cyclohexene-1-carboxaldehyde.